Composite bone graft device

ABSTRACT

A composite bone graft which comprises an allograft bone component; a synthetic bone substitute, wherein the synthetic bone substitute is in contact with the allograft bone component. The composite is arranged within a resorbable mesh casing.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.13/360,694, filed Jan. 28, 2012, which claims priority to U.S.Provisional Application Ser. No. 61/462,096, filed Jan. 28, 2011, eachof which is incorporated by reference in their entirety as if fully setforth herein.

FIELD OF THE INVENTION

The invention herein relates generally to the field of spinal fusion. Inparticular, this invention is drawn to a bone graft device andassociated methods of use.

BACKGROUND OF THE INVENTION

The spine can be considered to be a series of movable segments made upof vertebrae and discs. Due to trauma, disease, and/or aging, the spinemay be subject to degeneration. This degeneration may destabilize thespine and cause pain and/or nerve damage. Medical procedures are oftenrequired to either ease back pain, repair damage, or to prevent futuredamage.

One procedure that is often used to treat back pain or spinal damage isspinal fusion. Spinal fusion is a surgical technique used to combine (orfuse) two or more adjacent vertebrae. Supplemental bone tissue is usedin conjunction with the patient's natural osteoblastic processes in aspinal fusion procedure. Spinal fusion is used primarily to eliminateback pain caused by the motion of the damaged vertebrae by immobilizingadjacent vertebrae, reestablishing normal spinal column height andlordosis, and relieving pressure on spinal nerve roots. Conditions forwhich spinal fusion might be done include degenerative disc disease,treatment of a spinal tumor, a vertebral fracture, scoliosis, herniationof the disc, spondylolisthesis, or any other condition that causesinstability of the spine.

As a part of the procedure, bone or bone substitute grafts are commonlyplaced between the vertebrae following excision of a damaged spinaldisc, and topically along the posterolateral portion of the spine,adjacent to the pathologic segment. This helps induce bone growthbetween two adjacent vertebrae and fuses the facets in the posteriorspinal segments. Currently available synthetic bone grafts, however, aretypically not optimal and natural autologous bone grafts are in limitedin supply, while cadaveric or allograft bone grafts carry a risk ofdisease transmission. These grafts often collapse and/or resorb tooquickly, even in the presence of supplemental proteins such as bonemorphogenic protein (BMP), to encourage sufficient bone growth or goodquality, healthy bone formation.

While there are a number of products on the market that are in thecategory called “bone void fillers”, most if not all of them are clearedfor use as a standalone implant. However, there are specific situationsin supporting the formation of an arthrodesis (bony fusion) that requirean approach that is more malleable and shape retaining than granular orputty forms of bone void fillers.

There is therefore a need for a bone graft device that adequatelypromotes spinal fusion to treat degenerative disc disease and otherspinal conditions, while providing improvements over the prior methods.The disclosed invention embodies the combination of an allograftmaterial (i.e., cadaveric-derived bone chips or other bony forms) with asynthetic material which contains hydroxyapatite and gelatin in closeproximity and further contained in a pouch or bag that is permeable,which serves to hold the materials contained therein in place at thesite of bony pathology while remaining malleable during implantation.Graft migration, which can be a problem with current approaches usinggranular bone void fillers, is eliminated, ensuring that the graftmaterial will be resident at the site of repair. Additionally, there isa need for bone graft devices that can be attached to implanatableinstrumentation and introduced to an area of bone during surgery andadditionally do not migrate during surgery.

SUMMARY OF THE INVENTION

This invention provides a solution to the problems and disadvantagesdescribed above by providing a combined synthetic and natural bonematrix that promotes a solid fusion, controlled resorption of thematrix, and regeneration of a new fusion mass.

In one broad respect, this invention is a composite bone graft whichcomprises an allograft bone component and a synthetic bone substitute,wherein the synthetic bone substitute is in contact with the allograftbone component. The composite may include a mesh casing, wherein theallograft bone component and the synthetic bone substitute are disposedthrough (encased within) the mesh casing. In general, the graft is inthe form of a cylinder with an inner core and outer layer, and in oneembodiment the inner core is 5 to 15 mm in diameter and the outer layeris 2 to 15 mm in thickness. In one embodiment, the inner core iscomposed of the allograft bone component and the outer layer is composedof the synthetic bone substitute. In another embodiment, the inner coreis composed of the synthetic bone substitute and the outer layer iscomposed of the allograft bone component. In one embodiment, theallograft bone component and synthetic bone substitute are at leastpartially infused with an additive, wherein the additive is one or moreof platelet rich plasma, bone marrow aspirate, stem cells or otheradditive. In one embodiment, the composite bone graft is positionedwithin a bone graft syringe. The synthetic bone substitute can be, forexample, beta-tricalcium phosphate, hydroxyapetite,polyglycolic-polylactid acid, or poly-lactic acid. The allograft bonecan be in the form of dense cortical bone strips, packed bone chips, ordemineralized bone matrix.

In a further aspect, the disclosed invention embodies the combination ofan allograft material (i.e., cadaveric-derived bone chips or other bonyforms) with a synthetic material which contains hydroxyapatite andgelatin in close proximity of the allograft material and furthercontained in a pouch or bag that is permeable, which serves to hold thematerials contained therein in place at the site of bony pathology.

In another broad respect, this invention is a method of manufacturing acomposite bone graft, comprising forming an inner core and forming anouter layer of a different component around the inner layer. The innercore can be made of allograft bone component and the outer layer can bemade of a synthetic bone substitute. Alternatively, the inner core canbe made of a synthetic bone substitute and the outer layer can be madeof a allograft bone component.

In another broad respect, this invention is a method for using acomposite bone graft which comprises providing a bone graft syringehaving a composite bone graft disposed within the bone graft syringe;connecting the bone graft syringe to a delivery syringe, wherein thedelivery syringe is further described as containing an injectablecomponent selected from the group consisting of a cell concentrate, aplatelet rich plasma, a bone marrow aspirate, a clotting agent, andmixtures thereof; injecting the injectable component into the bone graftsyringe; and expelling the composite bone graft and the injectablecomponent from the bone graft syringe. This method can include the stepof filling a mesh casing with a composite bone graft.

In another broad respect, this invention is a composite bone graft kitwhich comprises a bone graft syringe and a composite bone graft disposedwithin the bone graft syringe, wherein the composite bone graft isfurther defined as having an allograft bone component and a syntheticbone substitute component. The kit can include a mesh casing. The kitcan also include a delivery syringe that connects to the bone graftsyringe for delivery of an injectable fluid such as cell concentrate, aplatelet rich plasma, a bone marrow aspirate, a clotting agent, andmixtures thereof. Thus, the kit can also include platelet rich plasma,bone marrow aspirate, stem cells, and combinations thereof.

In another broad respect, this invention is a method of treating aspine, comprising: applying topically a bone graft composite to aposterolateral portion of a spine. Alternatively, the bone graftcomposite is applied to an inner void of a fusion device, or applied toboth a spine and an inner void of a fusion device. The bone graftcomposite can be applied by ejecting the bone composite graft from abone graft syringe.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific features, aspects, and advantages of the present inventionwill become better understood with regard to the following description,appended claims, and accompanying drawings where:

FIGS. 1 and 2 illustrate cross-sectional views of cylindrical compositegraft in accordance with an embodiment of the invention;

FIG. 3 illustrates a cylindrical composite graft encased in anabsorbable mesh sheath in accordance with an embodiment of theinvention;

FIGS. 4 and 5 illustrate a cross sectional view and a perspective viewrespectively of a removable cap used in conjunction with a secondarysyringe for infusing a composite bone graft with an additive inaccordance with an embodiment of the invention; and

FIG. 6 shows a H-shaped mesh casing in accordance with an embodiment ofthe invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention relates a composite bone graft, composite bonegraft delivery kit and method for use.

Composite Bone Graft

The composite graft combines allograft or autograft bone and a syntheticbone substitute to form a composite graft that can be used as a topicalonlay for fusion grafting in, for example, the posterolateral gutters ofthe spine, across a fusion segment. The composite graft is formed priorto introduction into or onto the patient.

In one embodiment, the inner core of the graft may comprise a syntheticbone substitute material (which are sometimes referred to as bonescaffold materials), such as beta-tricalcium phosphate (BTCP),hydroxyapetite, polyglycolic-polylactid acid (PGLA), poly-lactic acid(PLA), or other synthetics. Allograft or autograft bone may be packedaround the synthetic core. The composite is typically formed inconcentric cylindrical shells. In one embodiment, the inner cylindricalshell is removed after the core and surrounding have been packed. Theallograft bone may take the form of dense cortical bone strips, packedbone chips, demineralized bone matrix, or other allograft boneformations. This composite graft may be placed in fluid contact withplatelet rich plasma, bone marrow aspirate, and/or stem cells. Thecomposite may also be treated with an appropriate supplemental clottingagent, such as thrombin or a solution containing Ca⁺ ions, to bind thecomposite graft together.

Alternatively, a composite graft may comprise an allograft or autograftbone inner core. This inner core may take the form of dense corticalbone strips, packed bone chips, demineralized bone matrix, or otherallograft bone formations. A synthetic bone substitute, in the form ofcompressed granules, strips, a pre-formed cylinder or powder, may bedistributed around the outside of the allograft core. This compositegraft may be placed in fluid contact with platelet rich plasma, bonemarrow aspirate, and/or stem cells. The composite may also be treatedwith an appropriate clotting agent, such as thrombin or a solutioncontaining calcium ions, to bind the composite graft together.

A composite graft provides a stronger construct than traditional bonegrafts with the potential for slower resorbsion and better boneformation. The synthetic core, or synthetic outer cylinder may bedesigned to have high surface area porosity or micro-channels to mimicnatural cancellous bone structure. In general, a high surface area is agreater than 3 fold increase in surface area over a traditionally usedcalcium phosphate. Traditional calcium phosphates have a surface area of1 m²/gram. A cancellous bone structure permits bone marrow to penetratethrough the bone graft. These characteristics provide for a compositebone graft that can be constructed to mimic natural bone having acortical outer layer, a cancellous inner layer.

A combination of synthetic and allograft or autograft bone materialshelps control resorption of the composite graft and improves thelongevity of the graft. These properties also help encourage bonegrowth. The composite graft facilitates stem cell differentiation andformation of a highly vascularized bone structure at an early stage ofremodeling, while maintaining a more stable structure for a longerperiod of time to promote better fusion.

A cross-sectional view of a composite 10 is shown in FIGS. 1 and 2. Thecomposite includes an outer layer 15 and inner core 20.

In another embodiment, the composite bone graft may be captured in aresorbable mesh casing. See in this regard FIG. 3. In FIG. 3, thecomposite bone graft 10 is surrounded by a resorbable mesh casing 25 tocreate a mesh encased composite bone graft 30. The mesh may help holdthe composite together and reduce the potential for the composite graftto dissipate prematurely or break apart before bone can form. The meshmay also be used to anchor the composite graft above and below thefusion site using suitable attachment means such as bone anchors orscrews. The mesh casing would typically be about the same size as thesyringe; however, it will be elongated when pulled putting the casingand graft in tension. Any biodegradable, biocompatible polymer orcopolymers, having resorbable properties may be used to construct thecasing. For example, PLA (polylactide), PGLA (copoly lacticacid/glycolic acid), and PLLA (poly-1-lactide) are representativepossible casing compositions. The configuration of the weave or thematerial composition may be varied to control resorption. The compositebone graft may have an allograft, or autograft inner core, or thesynthetic bone substitute material.

An embodiment of the invention includes a synthetic mesh bag, composedof PLGA or PLA, which are resorbable polymers in which the interior ofthe bag is fillable with bone void filler materials including one of thefollowing: cancellous chips, or demineralized bone, along with asynthetic hydroxyapatite/gelatin material. The openings of the bag areaccessed via a graft delivery device and will be closed by atie-mechanism (i.e., a suture). The bag is designed to be held in placeunder implantable surgical hardware or otherwise attached to pediclescrews, plates, rods, or any other surgical hardware.

In certain embodiments, the mesh bag is shaped in an “H” shape (FIG. 6).The “H” shape facilitates the placement and immobility of the implant.Additionally, the materials present therein will offer an optimalmicroenvironment for the formation of an arthrodesis. The containedmaterials also will be optimally saturable with a variety of surgicalfluids, including blood, bone marrow aspirate, bone marrow concentrateand other fluids autologously obtained during the surgical procedure.

In certain embodiments, the inventive device is composed of severalelements, including a fluid-permeable mesh bag composed of resorbable(PLGA, PLA) polymers, but whose pores are small enough to retain theallograft and synthetic components placed therein. The bag is designedso as to be accessible for filling with a variety of materials, whereinat least one type of allograft and a synthetic bone void filler arecombined and loaded into the interior of the mesh bag. One or more ofthe openings of the mesh bag are such that they can be closed bysuturing or other closure means, and the mesh bag itself can be attachedto hardware used in the surgical fixation of the spine. Additionally,the mesh bag can be created in a variety of shapes. In certainembodiments the mesh casing is composed of a first vertical tube-shapedstructure (V1) and a second vertical tube-shaped structure (V2). Incertain embodiments, the first and second vertical tube-shapedstructures are tranversely linked by a horizontal tube-shaped structure(H) to form an “H” shape. In the H-shaped structures, the horizontaltube-shaped structure is of a shorter length than the first and secondvertical tube-shaped structures. The “H-shaped” structures lendthemselves to being secured from migration when placed underneath thehardware used in a surgical repair of the spine (or other bonypathologies, like a long bone fracture). The materials intended forloading into the mesh bag are optimally capable of absorbing a varietyof surgical fluids, including autologous blood, bone marrow aspirate,bone marrow concentrate (BMC) and other autologous or sterile fluidsused during a surgical procedure, due in part to the presence of thesynthetic material which contains hydroxyapatite and gelatin. Theloading of the mesh bag can be accomplished by manual methods or one ormore of the openings of the mesh bag will be disposed to accept graftmaterial from a graft delivery device specifically designed to transfermaterial into the mesh bag. Wetting of the allograft/synthetic bone voidfiller materials can be accomplished once the dry materials are loadedinto the mesh bag or after the dry materials are placed in contact withthe surgical fluid(s), including BMC, and then transferred to theinterior of the mesh bag. If loaded with dry material, the filled bagcan be placed into contact with a bulk autologous or sterile fluid andallowed to sit in contact for an appropriate amount of time to achievewetting of the dry materials.

The device can be placed in the site of pathology by simply transferringthe filled device into the appropriate site, attached as appropriate orseated beneath any hardware used in the spinal fusion procedure.Openings of the mesh bag can be sutured closed or otherwise sealed priorto or after the mesh bag has been implanted.

Composite Bone Graft Kit

A composite bone graft kit may comprise a conventional bone graftsyringe containing a synthetic core within the syringe body. A bonesyringe is typically about 1.5 cm in diameter and 10 cm in length.Depending on the addition of diluents for clotting and cell adhesion,the composite is typically expelled allowing it to maintain acylindrical shape as it fills the casing or is cut to desired length.The synthetic core may be surrounded by bone chips or other autograft orallograft bone components. As an example, the syringe may carry a 5-15mm diameter synthetic core surrounded by a 2-15 mm thick bone chip outerlayer. The resulting construct can have a total diameter of from 7 mm to3 cm. In certain embodiments, the core has a diameter of 5-10 mm or10-15 mm. In certain embodiments, the outer layer has a diameter of 2-5mm or 5-15 mm. For example, the volume of the composite can be about 75percent core and 25 percent outer layer. The total amount of bone graftcomposite to be delivered in the syringe is typically 15 to 20 cubiccentimeters (cc). In general the composite has a length in the syringeof from 8 to 10 centimeters (cm). As applied the composite may cover awide variety of surface sizes. In one embodiment, the core moresimilarly relates to cortical bone with the core more similarly relatingto cancellous bone, thus defining to different, defined regions of thecomposite, as contrasted with an admixture. The proportions and quantityof synthetic and allograft bone material may vary. Alternatively, thekit may comprise a bone graft syringe comprising an autograft orallograft bone core surrounded by a synthetic material.

In one embodiment, at least one end of the syringe has a mechanism toallow platelet rich plasma, bone marrow aspirate, stem cells, and/orclotting agent(s) to enter the syringe and contact the composite graft.For example, a removable cap may be positioned at one end of thesyringe. The cap may contain one or more ports for the sequential orsimultaneous injection of one or more components (additives such asplatelet rich plasma) from a secondary source. See in this regard, FIG.4 and which depict a removable cap 40 that includes a 3 way valve(multi-lumen port) that corresponds to three channels for injection ofthe platelet rich plasma, bone marrow aspirate, stem cells, clottingagents, and/or other additives into the inner layer 15 and/or outerlayer 20 of the composite 10. The secondary source of injection may takethe form of a secondary syringe that connects to the cap 40 to beco-injected with the composite or injected into the bone graft syringeprior to injection of composite. Alternatively, the composite can beplaced in contact with or mixed with the additives prior to thecomposite being positioned in the bone graft syringe.

Methods for Use

In a sterile field, a bone graft syringe comprising a combination ofsynthetic and allograft or autograft bone is connected to a secondarysource containing a stem cell concentrate. The secondary source may takethe form of a second syringe. The stem cell concentrate is usuallyinjected into the bone graft syringe from the top and the compositegraft absorbs the stem cell concentrate. The bone graft syringe may alsobe connected to a secondary source for the purposes of injectingplatelet rich plasma, bone marrow aspirate, or clotting agent(s).Alternatively, two or more secondary sources may be connected to thebone graft syringe simultaneously. This allows for simultaneousinjection of any of the following: platelet rich plasma, bone marrowaspirate, clotting agent(s), and/or other additives. These componentsmay be injected into the bone graft syringe in any order, simultaneouslyor sequentially. In a preferred embodiment, a Y-shaped adapter isconnected to the bone graft syringe to permit the simultaneous injectionof stem cell concentrate and a clotting agent until the composite graftis fully saturated.

The bone graft syringe should sit to allow the composite graft to absorbany injected components. The natural “wicking” effect of the materials,combined with injection pressure and gravity, is usually adequate toensure uniform mixing. Alternatively, a vacuum may be applied to “pull”the injected components into the composite bone graft.

Using the plunger, the composite graft is then expelled and ifnecessary, may be cut to an appropriate length for clinical application.The composite graft is then topically applied and molded along theposterolateral gutters of the spine, or other areas of the spine toensure intimate contact to the prepared bone bed across a fusionsegment. The composite would typically be used in lumbar regions, andpotentially in thoracic regions depending on the circumstances. Multiplecomposite grafts could be used in a given procedure. The compositegrafts could also be applied to an inner space that may be present incertain types of fusion implant devices.

In certain embodiments, the bone graft composite of the claimedinvention is attached to an implantable surgical instrument and appliedto an area of bone. This type of implanatation can be done in any typeof bone. A specific type of example is the application of the bone graftcomposite to the posterolateral portion of the spine. In certain cases,the bone graft composite can be applied to an area of bony pathologysuch as area where there is a gap in the bone or in an area between twobones.

Although illustrative embodiments have been shown and described, a widerange of modifications, changes, and substitutions are contemplated inthe foregoing disclosure and in some instances, some features of theembodiments may be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theembodiments disclosed herein.

What is claimed is:
 1. A composite bone graft comprising: an allograftbone component; a synthetic bone substitute, wherein the synthetic bonesubstitute is in contact with the allograft bone component; and aresorbable mesh casing disposed around the allograft bone component andthe synthetic bone substitute, wherein the resorbable mesh casing holdsthe composite bone graft together, and wherein the mesh casing comprisesa first vertical tube-shaped structure and a second vertical tube-shapedstructure that are transversely linked by a horizontal tube-shapedstructure.
 2. The composite bone graft of claim 1, wherein the allograftbone component forms an inner core and the synthetic bone substituteforms an outer layer around the allograft bone component.
 3. Thecomposite bone graft of claim 1, wherein the synthetic bone substituteforms an inner core and the allograft bone component forms an outerlayer around the synthetic bone substitute.
 4. The composite bone graftof claim 1, wherein at least one of the allograft bone component and thesynthetic bone substitute are at least partially infused with anadditive comprising one or more of a platelet rich plasma, bone marrowaspirate, and stem cells.
 5. The composite bone graft of claim 1,wherein: the synthetic bone substitute is a mixture of hydroxyapatiteand gelatin; and wherein the allograft bone component comprises at leastone of dense cortical bone strips, packed bone chips, or demineralizedbone matrix.